Whether or not union slush funds were used to pay for renovations at former prime minister Julia Gillard's house in the early 1990s could come down to the word of two builders and a former union official who will appear before the royal commission into trade unions this week.

Melbourne builder Konstantinos Spyridis will provide evidence about building work he did at the offices of the Australian Workers Union in Carlton and at Ms Gillard's property in the Melbourne suburb of Abbotsford.

He says Ms Gillard paid for all the work he carried out at her Abbotsford property in 1994, according to Jeremy Stoljar, counsel assisting the royal commission into trade union governance and corruption.

Another builder, Athol James, who helped with renovations at the house, will allege he saw Ms Gillard's former boyfriend, Bruce Wilson, hand cash to Ms Gillard to pay him for his work.

Wayne Hem, a former employee of the Australian Workers Union, will claim he deposited $5000 in cash into Ms Gillard's bank account at the request of Mr Wilson.

Mr Stoljar said evidence to be put to the commission suggests money from a union slush fund linked to the AWU was used to pay in part for the purchase of a house in Kerr Street for Mr Wilson. ''This point does not seem controversial,'' he said.

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However, he was less confident about the facts surrounding allegations that union slush fund money was used to pay for Ms Gillard's home renovations. ''There is factual controversy about this,'' he said.

Mr Stoljar will submit Mr Wilson should face criminal charges for conspiring with former AWU official and self-confessed bagman Ralph Blewitt to create a secret slush fund to issue false invoices for services never rendered.

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In May, Mr Blewitt told the royal commission he used $7000 from a union ''slush fund'' to pay for renovations to Ms Gillard's house. Mr Blewitt, who has confessed to fraud, alleged he attended Ms Gillard's home in 1994 and handed $7000 to a builder.

He said Ms Gillard was home that day but was not in the room when he handed over the cash.

The first witness to appear before the royal commission on Tuesday was Ian Cambridge, a commissioner for the Fair Work Commission who was an AWU official in the 1990s.

Mr Cambridge recalled a meeting of the AWU's finance committee on August 2, 1995, when he confronted Mr Wilson about the AWU Members Welfare Account.

''It was clear in the meeting that Mr Wilson had mixed private monies for slush funds with AWU funds, which is strictly prohibited,'' Mr Cambridge said in evidence.

Mr Cambridge said at that time he was not aware of the AWU Workplace Reform Association, which operated as a slush fund.

Mr Cambridge said he was ''infuriated'' when $250,000 that should have gone to the union's bereavement fund was instead earmarked for redundancy payments for Mr Wilson and other union officials, which would have delayed bereavement payments for six months.

Ms Gillard has said she was confident she had paid for the renovations on her home.